1. Field of the Invention
The present invention relates to a doze prevention system used for drivers of vehicles, operators of radar monitoring stations, and the like, wherein the waveform of eyeblink of the operator is analyzed to detect a "sleepiness" state so that the operator is alerted by an acoustic alarm signal upon detection of a certain waveform before the operator falls into a doze.
2. Description of the Prior Art
One prior art drowsiness alarm system is shown in FIG. 1. The system includes a steering handle 10 of a vehicle or the like operated by a driver 11 of the vehicle, a steering angle detector 12, an awake-state pattern generator 13, a comparator 14 which compares the pattern of the current steering operation with the pattern in an awake state provided by the pattern generator 13, and an alert device 15 which produces an acoustic alarm signal in response to the output of the comparator 14.
The operation of the foregoing system will be described in the following. During a normal drive of a vehicle by the driver 11 in awake condition, small steering operations take place uninterruptedly even if the vehicle is driven on a straight course. The steering operations are detected by the steering angle detector 12, and the number of steering operations in unit time length, e.g., one minute, and the angle of each operation are recorded as an awake-state pattern of operation by the awake-state pattern generator 13. If the driver has entered a "sleepiness" condition or even has fallen into a doze, the steering operation becomes coarse and the number of steering operations decrease. Consequently, such a driver's condition appears as a decrease in the number of steering operations and an increase in the steering angle operated at each operation. The system is operated during a run of the vehicle so as to measure the steering angle by the detector 12 and count the number of steering operations in unit time length, and these values are compared by the comparator 13 with the reference values of the awake condition which have been determined in advance by the awake-state pattern generator 13. If an operational pattern specific to "doze driving" as mentioned above is detected, the comparator 14 issues a command to the alert device 15, which in turn produces an acoustic alarm signal so as to make the driver aware of the drowsy condition.
U.S. Pat. No. 4,359,724 discloses another alertness detecting system wherein the interval between successive eyeblink pulses in an eyeblink waveform is monitored, and if excessive, results in sounding an alarm.
The foregoing conventional doze prevention systems, however, do not operate satisfactorily to detect the driver's critical mental condition in a practical sense due to different individual behaviors of steering operation and eyeblink intervals by each driver. In addition, these conventional systems have a serious drawback that acoustic alarms are produced only after extended delays during which an accident or events leading to an accident could already have occurred.